Collision-induced (2)P(1/2) - (2)P(3/2) mixing in sodium

The total cross sections for Inelastic collisions between excited sodium and noble gas atoms in their ground states, leading to 2 2 3 P^y2 — — 3 ^3/2 excitation transfer in sodium, have been determined in a series of sensitized fluorescence experiments with pure sodium vapour and its mixtures with noble gases. In the experiments with pure sodium, the sodium vapour pressure was varied over the range 0 1.6 x 10 ̂mm Hg, where radiation trapping effects were negligible and the 2 2 cross section Q2(3 P^yg — 3 P^yg), for Na Na collisions, was found to be 283 + 10 per cent. In the sodium-noble gas experiments the sodium vapour was maintained at a pressure of 5 x 10 ̂mm Hg and the noble gas pressures ranged from 0 to 1 mm Hg. The cross sections Q i{3^Pi/2 ̂— ^^^^3/2^ "^^^^3/2^ follows; Na He, 86.0 and 44.8 Na Ne, 67.0 and 35.4 Na Ar, 110 and 55.9 Na Kr, 85.0 and 43.6 X^; Na Xe, 89.8 and 45.6 X^, all quoted with an accuracy of + 5 per cent. The ratios Q]^/Q2 in agreement with the value predicted from the principle of detailed balancing and the cross sections also agree, as to order of magnitude, with some theoretically predicted values.